Selective receiving system



` UVCII llllll UR ls11201055 H.`-Wl NIQHOLS. SELECTIVE RECEIVING SYSTEM` APPLICATION FILED DEC. I8, I920.

Patented June 20, 1922.v

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UNITED STATES PATENT OFFICE.

HAROLD W. NICHOLS, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SELECTIVE RECEIVING SYSTEM.

Specification of Letters Patent.

Patented June 20, 1922.

T0 all lwilma t may concern.'

Be it known that I, HAROLD WV. NICHOLS, a citizen of the United States, residing at Maplewood, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Selective Receiving Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to a selective re ceiving system and more particularly to a radio receiving arrangement employing multiple detection.

When a receiving station adapted to cooperate with a low-power or weak transmitting station, receives energy from a high power or strong transmitting station, interference results, the measure of which is determined by the intensity of the signal current received from the strong7 station relative to that from the weak station and to some extent upon the relative frequencies of the waves radiated from the two transmitting stations. Hence, when two such stations employ frequencies which are close together on a percentage basis, i. e., the ratio of the frequency of the interfering to selected waves is large or that of theclif ference frequency relatively to that of the desired waves is small, selection at the receiving station of the signal currents radiated from the weak transmitting station is extremely difficult with the arrange ments heretofore devised.

The'primary object of thisinvention is to provide an arrangement which is selective of a current of low intensity compared to a strong interfering wave of frequency relatively close to that of the current to be selected.

Another object is toprovide means for eliminating interference due to a current of large amplitude relative to that of the current which it is desired to receive.

.A further object is to provide a selective arrangement of this type which employs multiple detection.

In this system advantage is taken of the fact that because of the curved characteristic of most detectors including the vacuum tube type, if a speech or other signal modulator carrier current is impressed on its input circuit there will be present in the output circuit the signal modulated first even harmonic of the carrier frequency and by tuning the output circuit of the detector andb the coupled input circuit of the next detector to this first even harmonic considerable selectivity will be obtained.

According to the present invention the carrier wave received is impressed upon the tuned input circuit of a detector device from the output circuit of which the first even harmonic of the carrier frequency is selected and applied to the input circuit of a second detector device from the output circuit of which, in turn, the second even harmonic frequency of the carrier vwave is selected. This process may be continued for any desired number of stages and the detected audio frequency signal current of the last stage is supplied to a telephone receiver or other indicator, The various stages may, if desired, be connected by amplifying devices.

Thus, an incoming signal modulated carrier frequency wave may be represented by the formula A(l-}c cos. qa t) sin. mt or by the three component sine frequencies A sin.

which A is an amplitude factor, sin. @t is the instantanteous value of the carrier frequency current (wherein @22aj', f being the frequency), sin. cpt is the value'of the tot;

current of signal frequency at any instantA (where cz27rf, f being the frequency and is a constant. If this current is impressed on the grid circuit of a detector, the output current is given by the equation 2B [EB-Hi. IEC-HLA (l-Hc cos cpt) sin @t4-KH or, taking Bzland EB-Hr EC-i-Kzd, then zw A (lq-"lt" cos cpt) sin cH-0Q2. In these two equations B is a constant, ER is the plate battery potential n is the amplifying factor of the tube, E.; is the polarizing potential applied to the grid, K is a constant and the other characters are the same as in .the preceding formula.

Simplifying these expressions and neglecting co-efficients we get, in addition to the efficients) cos 4oz?, cos 4 1 -1q )t,cos (4-i-2cp) t, cos (4-}-3q2)t and cos (4w-}-4 p), which is a second even harmonic of the carrier frequency. Similarly, We can tune for the frequency 4m and detect again and so on or We can get the signal frequency in this or any other outputcircuit and impress it across a signal indicating device.

It is to be noted that in the plate circuit of the first detector the amplitude of the signal frequency varies as A2, in the plate circuit of the second detector as A4, in the plate circuit of the third detector as As and so on; A being the amplitude of the incoming modulated carrier Wave.

Where a different harmonic frequency is selected the amplitude factor of the signal frequency will increase by a correspondingly different power.

The operation of a system involving this invention may be understood by reference to the following detailed description taken in conjunction with the attached drawing in Which Fig. 1 diagrammatically illustrates a simple circuit arrangement embodying a multiplicity of stages of detection, Fig. 2 shows a tivo-stage detection arrangement and includes a high frequency amplifier, the amplifier and detectors being shown diagrammatically and Fig. 3 shows an arrangement involving three stages of detection, and a plurality of stages of amplification for both the high frequency and the audio frequency currents.

Referring to Fig. 1, an antenna 1 tuned to the frequency of the incoming Waves is inductively coupled to a resonant circuit 2, also selective of the carrier frequency, Which is connected to the input terminals of the detector 3. The detector herein shown, by Way of example, as a three-elementvacuum tube has included in its plate circuit a selective circuit- 4 tuned to the first even harmonic of the frequency of the incoming carrier Waves.

Inductively associated with the circuit 4 is a resonantcircuit 5, tuned to the same frequency as circuit 4, Which is connected to the input terminals of a detector 6, Whose output circuit includes a circuit 7 selective of the second even harmonic of the carrier frequency. Current of the harmonic frequency selected by circuit 7 is transferred to a similarly tuned circuit 8 by the transformer interconnecting them and is impressed across the input circuit of a third detector.

As herein indicated this may be a detector 9, or other stages of detection may be introduced, in Which event, the circuit- 8 will be connected across the input of a. succeeding detector and its output circuit will include a resonant circuit tuned to a harmonic of the frequency of circuit 8. Finally, a selective circuit tuned to the same frequency as that included in the output circuit of the detector which precedes the device 9 will be included in the input circuit of the last detector, the output current of which Will be impressed across the signal indicating device herein shown by Way of example as a telephone receiver.

Heating current for the filaments of the detecting tubes may be supplied from a single source or a separate battery for this purpose may be associated with each filament. In like manner plate current for the tubes may be provided from a single source or a separate battery may be associated with each tube out-put circuit as here-in shown.

In either case, reta-rd coils 10 and blocking condensers 11 should be inserted in the output circuits of the tubes to prevent shortcircuiting of the source or sources of supply of plate current and the flow of direct current from said sources to the selective circuits associated With them. The blocking condense-rs are designed to permit the flow of the variable currents to said tuned circuits While preventing the flow of direct current thereto. In this, as Well as in the following figures, a condenser 12 may be used in shuntto the receiver 12 for the purpose of by-passing any high frequency current, that is, any current 0f carrier or like frequency Which may be present in the receiver circuit.

Referring to Fig. 2, the antenna 13 and the circuit 14 inductively associated with it are tuned to the frequency of the incoming Waves. Circuit 14 is connected across the input circuit of the amplifier 15 and the output circuit of the latter to the input circuit of a detector 16 Whose output circuit includes the resonant circuit 17 tuned to the first even harmonic of the frequency of the signal Waves. Inductively associated with this circuit 17 is a circuit 18 selective of the same frequency, which is adapted to impress the selected oscillations across the input circuit of the detector 19, Whose output circuit is connected to the telephone receiver 21 by means of the transformer 20.

In Fig. 3, the antenna 22 is associa-ted with a resonant circuit 23 tuned to the frequency of the incoming signal modulated waves. The high frequency current is amplified by a three-stage amplifying system including the amplifiers 24, 25 and 26 and detected by the detector 27 which includes in its output circuit the circuit 28 tuned to the first even harmonic frequency of the incoming Waves. The latter circuit is inductively associated with the circuit 29 selective of the same frequency, whereby the selected oscillations are transmitted thereto and impressed across the input circuit of the amplifier 30. The variable current in the output circuit of the Tube S0 is amplified by devices 31 and 32 and impressed across the input circuit of the detector 33, the output circuit of which inpressedV upon the input circuits of the sevcludes the circuit 34 timed to the first even eral detectors progressively increase from harmonic of the current traversing its input carrier frequency supplied to the first detec` circuit, i. e., the second even harmonic of the tor to the 1st, 2nd, 4th, 8th, etc., even power 5 carrier frequency. harmonic thereof supplied to the last of the rIlhe current selected by the circuit 34 is series. transferred to the resonant circuit 35 timed In another aspect, the detectors may be to the same frequency which is connected considered as relay devices which serve to across the input circuit of the'detector 36. initiate in their output circuits oscillations After amplification by the amplifiers 37 and which are a harmonic frequency of that sup- 7 38 this current is transmitted through the plied to their input circuits. transformer or repeating coil 39 to the re In an arrangement of this kind the circeiver 40. cuits may tend to sing or oscillate because In passing it is to be noted that the input of the harmonically tuned input and voutput circuit of each detector is provided with a circuits. This may be overcome by using leak-path 4l comprising a high resistance short twisted leads, making the timed cirshunted by a condenser. cuits of small inductance and large capacity In the last two figures, no reference has and using suitable choke coils in the plate been made to the sources of supply for the circuits of the vacuum tube devices. various thermionic devices or the retard coils From the preceding description, it will be and blocking condensers which'are essential apparent that an arrangement has been deto their proper operation, but it is to be unvised employing multiple detection having derstood that these well-known features are a series of detectors connected by tuned cireniployed in a manner which it is believed cuits selective of a harmonic frequency of will be obvious from Fig. 3 in which they the preceding stage of detection and Which are shown. In this figure the condensers 42 is independent of the particular means emare introduced to eliminate or suppress ployed to effect this condition. i noises due to the operation 0f the supply It is therefore to be understood that this source across which they are bridged, invention. is not limited tothe specific de- Whether it be a battery 0r a direct Current tails herein shown and described but only by generator.

It may be stated that multiple detection is more selective than single detection and for the scope of the attached claims.

What is claimed is: l. lA method of selective signal reception large frequency differences between the cur Which COmplSGS ClGtBCIlg llCOIIliIlg IHOClurent transmitted by the station whose waves lated Signal WWGS SGIQCHg il hEIIIIlOIlC freit is desired to receive and the interfering queney of said waves, detecting said waves station, a large number of stages of detecof selected frequency and indicating the tion is more selective than a lesser number, modulating waves.

or apparently than the heterodyne interme- 2. A method of signal reception which indiate frequency method; but for a small frevolves multiple detection of modulated sigquency difference, which is usually desired, nal waves by selecting and detecting a proa large number of stages is less selective gressively increasing` harmonic frequency at than a small number or apparently than the each stage of detection and indicating the heterodyne intermediate frequency method. signal waves.

The reason that for small frequency differ- 3. A method of selecting modulating curences a large number of stages is less selecrenty impressed upon a carrier of given fretive than a smaller number is that the amquency from an interfering signal current plitude of the signal current in the output which modulates a carrier of different freof each stage varies as the square of the amquency, which comprises impressing both inplitude in the input of that stage, so that if coming waves upon a circuit selective of the A is the amplitude of the carrier frequency, desired frequency, controlling by means of for double detection the amplitude of the the waves in said circuit an independent signal current will vary as A4 and for triple source of energy to initiate oscillations which detection as A8. Thus, for a strong interferare a harmonic of said selected frequency` ing transmitter the amplitude of the interselecting said harmonic frequency waves and fering current as compared with that of the controlling by means of the waves of harsignal current which it is desired to receive monic frequency an independent source of will be greater the greater the number of energy to initiate oscillations which are a stages, for a given ratio of energy received armonie of the above-mentioned harmonic from the interfering to that from the de requency. sired transmitter. A signal receiving system for a modu- In the arrangementhereinbefore described lated carrier wave comprising a plurality several detectors are connected in cascade by of detectors and selective circuits interconmeans of the interconnecting selective cirnecting said detectors in cascade tuned to a cuits between them and the frequencies imharmonic of the frequency of the Wave traversing the preceding interconnecting cir-V cuits and means to indicate the modulating current.

5. A radio receiving system for a modulated carrier current comprising means for selecting and impressing said carrier current upon the input circuit of a detector, means in the output circuit of said detector for select-ing a harmonic of the carrier frequency, means for impressing said harmonic frequency 0n the input circuit of a second detector and means associated with the output circuit of said second detector to indicate the modulating current.

6. A radio receiving system comprising means to select a modulated carrier current and impress it upon the input circuit of the first of a plurality of detectors connected in cascade, means between each pair of detectors for selecting a harmonic frequency7 of the oscillations impressed across the inputI circuit of the preceding detector of the pair, means to impress said selected oscillations on the input circuit of the succeeding detector of said pair and means associated with the output circuit of the last detector of the series for indicating the modulating current.

7. A radio receiving system comprising means to select a modulated carrier current and impress it upon the input circuit'of the first of a plurality of detectors connected in cascade, means het-Ween the detectors for selecting from the output circuit of the first and impressing upon the input circuit of the second detector a harmonic of the frequency of the current impressed upon the input circuit of therst detectorand means associated with the second detector for indicating the signal current.

8. A selective radio system comprising a plurality of detectors, means connecting said detectors in cascade each adapted to select a progressively increasingharmonic of the incoming' modulated Waves and lmeans connected to the last detector of the series for indicating the signal current.

9. A radio receiving system comprising a plurality of detectors connected in cascade, each having its output circuit selective of a harmonic frequency of the current supplied to its input circuit and signal indicating means associated With the last of said detectors.

10. A radio receiving system comprising a circuit selective of the incoming signal Waves, a plurality of relay devices connected in cascade adapted to initiate oscillations of successively increasing harmonic frequencies in the circuits interconnecting them and a signal indicating means associated With the last relay.

11. A method of selective signal reception which comprises selectively receiving incoming carrier Waves, and progressively increasing their frequency and selecting Waves of increasing frequency in alternate steps.

12. A method of selective signal reception Which comprises selectively receiving incoming carrier Waves, increasing their frequency in steps and selecting Waves of successively increased frequency.

18. A selective radio receiving system comprising means to selectively receive incoming carrier Waves, means to increase progressively the frequency of said Waves, and means to select waves of increased frequency alternating With said frequency increasing means.

14. A selective radio receiving system comprising means to selectively receive incoming Waves, means to increase their frequency in steps having means to select Waves of successively increasing frequency.

15. A selective radio receiving system comprising means to selectively receive incoming carrier Waves, means to increase progressively the frequency of said Waves including successive resonant circuits tuned to increased frequencies.

In Witness whereof, I hereunto subscribe my name this 16th day of December, A. D.,

' HAROLD W. NICHOLS. 

